Virginia Law

A. Diatomaceous earth filtration shall be limited to treatment of a surface water source, a GUDI source, or both with low turbidity and low bacterial contamination, and may be used for iron removal from groundwater.

B. Pilot plant study. Installation of a diatomaceous earth filtration system shall be preceded by a pilot plant study on the water to be treated.

C. Types of filters. Pressure or vacuum diatomaceous earth filtration units will be considered for approval.

D. Treated water storage. Treated water storage capacity in excess of normal requirements shall be provided to:

1. Allow operation of the filters at a uniform rate during all conditions of system demand at or below the approved filtration rate, and

2. Guarantee continuity of service during adverse source water conditions without bypassing the system.

E. Number of units. At least two filtering units shall be provided at plants having a rated capacity of more than 100 gpm.

F. Precoat.

1. Application. A uniform precoat shall be applied hydraulically to each septum by introducing a slurry to the tank influent line and employing a filter-to-waste or recirculation system.

2. Quantity. Diatomaceous earth in the amount of 0.2 lb/ft² of filter area.

G. Body feed. A body feed system to apply additional amounts of diatomaceous earth slurry during the filter run is required.

1. Quantity. Rate of body feed is dependent on source water quality and characteristics and must be determined in the pilot plant study.

2. Adequate accessibility to the feed system and slurry lines is required.

3. Continuous mixing of the body feed slurry is required.

4. Consideration should be given to providing a coagulant coating (alum or suitable polymer) of the body feed.

H. Rate of filtration. The hydraulic loading rate shall not exceed 1.5 gpm/ft² of filter area. The filtration rate shall be controlled.

I. Head loss. The head loss shall not exceed 30 psi for pressure diatomaceous earth filters, or a vacuum of 15 inches of mercury for a vacuum system.

J. Recirculation. A recirculation or holding pump shall be employed to maintain a differential pressure across the filter when the unit is not in operation to prevent the filter cake from dropping off the filter elements. A minimum recirculation rate of 0.1 gpm/ft§ filter area shall be provided.

K. Septum or filter element. The filter elements shall be structurally capable of withstanding maximum pressure and velocity variations during filtration and backwash cycles, and shall be spaced so that no less than one inch is provided between elements or between any element and a wall. Means shall be provided to check the septum for cleanliness or damage. Consideration should be given to providing septum assemblies where an individual septum can be removed, cleaned, repaired, and replaced.

L. Inlet design. The filter influent shall be designed to prevent scour of the diatomaceous earth from the filter element.

M. Backwash. Provision shall be made for periodic backwashing of the filter. A satisfactory method to thoroughly remove and dispose of spent filter cake shall be provided.

N. Appurtenances. The following shall be provided for every filter:

1. Sampling taps for source and filtered water;

2. A loss-of-head or a differential pressure gauge;

3. A rate-of-flow indicator, preferable with totalizer; and

4. A throttling valve used to reduce rates below normal during adverse source water conditions.

O. Turbidity monitoring. Indicating and recording turbidimeters meeting requirements of 12VAC5-590-770 B shall be provided for:

1. The source water;

2. The effluent from each filter unit; and

3. The CFE.

P. An operation and maintenance manual shall be provided for all diatomaceous earth filtration units. The manual shall include the following:

1. A detailed description of the treatment units and the control of each unit for optimal performance;

2. A preventative maintenance schedule;

3. The manual adjustment and override procedures for all automatic control features; and

4. A troubleshooting guide for typical problems.

Q. The owner shall require the equipment manufacturer to provide onsite start-up and follow-up training.